A variable pitch pulley, VPP, installed on a motor to drive a fan pulley provides a means for varying the volume of air produced by a fan. The change in the air volume is accomplished by changing the operating position of the pulley. Depending on the perceived position of the belt in the groove of the pulley, a VPP is characterized as operating in either one of the three modes: full open, closed, or in a middle position. However, this qualitative description of the operating characteristic of a pulley is limited and inaccurate since pulleys can operate in as many as 14 positions depending on its size and the width of the v-belt.
To change the air volume produced by a fan and air ducted into a room, a contractor typically first must access the air handling unit, which may be mounted on the roof of a building. Accordingly, the contractor must gain access to the roof of a building and locate the air handling unit. The contractor then opens a compartment on the air handling unit to disassemble the motor VPP that drives the fan pulley, change the operating position of the VPP, re-assemble the VPP, and close the compartment. Thereafter, the contractor returns to the room and reads the airflow. If the airflow is still inadequate, the contractor must repeat the above process until the desired airflow is achieved. If the air volume cannot be achieved with the pulley already installed, the contractor must buy and install a pulley of a different size and then repeat the above process. Eventually, after the contractor achieves the desired airflow, he must make a final trip to the roof to obtain data from the air handling unit for a report. Then, the contractor inaccurately will report that the VPP is operating in either a full open, closed, or middle position. The present process of changing airflow is laborious, antiquated, slow, and inefficient. Accordingly, there is a need for an efficient means for adjusting airflow and preferably a one step process for adjusting airflow.
Furthermore, there generally is no provision for checking the operating position of a pulley against the belt installed to drive it. More specifically, there are gauges including feeler gauges specifically for measuring the operating circumference of pulleys. Some instruments are available specifically for measuring the wear of the tapered portion of pulleys. There also are calipers, rulers, and tapes for measuring distances and depths with a high degree of accuracy. However, none of these devices measure the operating position of a VPP or verify the use of an adequate belt.
As shown in FIG. 5, a VPP 50 is made of two opposing sheaves 52 and 58. Sheave 52 is secured to the shaft of a motor by means of a removable key, and sheave 58 is secured to the hub 56 of sheave 52 by means of two removable keys formed at 180 degrees apart. The hub 56 of sheave 52 is threaded, thereby providing a track on which sheave 58 moves by rotation. Sheave 58 moves towards or away from sheave 52 by increments of 180 degrees (i.e., a ½ turn). Each of the half turns that comprises the functional length that sheave 58 rides on the hub 56 of sheave 52 represents an operating position of VPP 50. The number of half turns or operating positions of VPP 50 varies by the size of the pulley and belt used to drive VPP 50.
The sides of the sheaves 52, 58 facing each other are formed of tapered portions 62, 64, respectively, beginning from the rims 66, 68 of the sheaves 52, 58, respectively, and transitioning to flat portions 54, 60, of the sheaves 52, 58, respectively, towards the hub 56. The flat portions 54, 60 of the sheaves 52, 58 are parallel to each other. The tapered portions 62, 64 of the sheaves 52, 58 conform to the tapered shape of v-belts that connects the VPP 50 and fan pulley. Accordingly, the tapered portion of the v-belt makes full contact with the tapered portions 62, 64 of the sheaves 52, 58. V-belts come in a plurality of widths, thereby limiting the VPP 50 to a predetermined operating position for the v-belt to maintain full contact with the tapered portion of the VPP 50. Otherwise, the equipment driven by the pulley would perform poorly and the belt would fail prematurely. The use of a wrong belt is one of the primary causes of belts failing prematurely.